The present invention relates to a method for controlling the ignition energy in an internal combustion engine whereby the amount of ignition energy conducted to an ignition coil is stabilized while the problem of excess heat in the ignition coil is effectively reduced.
The conventional system for controlling the ignition energy supplied to an internal combustion engine utilizes a switch to supply current to a primary winding of an ignition coil during the time that a distributor crank shaft of the engine is rotated over a predetermined crank angle. In this simple system, the time period during which current is supplied to the primary winding of the ignition coil varies inversely with the rotational speed of the engine. Thus, as the rotational speed of the engine is increased, the time period during which current is conducted through the primary winding is shortened, the ignition energy supplied to the engine decreases, and the ignition capacity is diminished. Conversely, when the rotational speed decreases, current through the primary winding is conducted over a longer time period and the ignition capacity increases. However, during low speed operation, the current is conducted over such a long period of time that excessive heat is generated in the ignition coil. Excessive heat is also produced in power transistors which are used in some conventional ignition systems to switch on and off the current which is supplied to the primary winding.
One known system which has been developed in an attempt to solve the above-mentioned problems utilizes electronic circuitry to control the current flowing through the primary winding of the ignition coil, so that the time period during which it flows is always held constant. However, this type of system produces ignition energy in an amount which disadvantageously varies in accordance with the voltage applied to the primary winding of the ignition coil. In general, the ignition energy is proportional to the square of the voltage applied to the ignition coil. Thus, if the voltage applied to the ignition coil changes from 6 V to 18 V, the ignition energy will increase by a factor of approximately eight or nine. Therefore, if the ignition coil is designed so that sufficient ignition energy is produced when a low voltage is applied to its primary winding, an excessive amount of harmful heat energy will be produced in the coil when the primary winding voltage becomes high.
It is, therefore, a primary object of the invention to provide an ignition energy control method for providing adequate ignition energy during high speed rotation of an engine, while reducing the amount of heat generated in an ignition coil during low speed rotation of the engine.
It is another object of the invention to provide an ignition energy control method which provides adequate ignition energy to the engine for a predetermined range of voltage applied to the primary winding of the ignition coil.
It is a further object of the invention to provide an ignition energy control method whereby ignition energy supplied to an engine can be controlled by using a digital computer having small storage capacity.